1. Field of the Invention
The present invention pertains to an optical gas-analysis system, and more particularly relates to an optical gas-analysis system suitable for an in-line analysis system of a process chamber that uses a gas in a semiconductor manufacturing equipment and the like, and a gas flow cell used in the optical gas-analysis system.
2. Description of the Related Art
In an earlier multiple-reflection cell of Herriot type, as illustrated in FIGS. 11 and 12, opposite two mirrors of first cell mirror 41 and second cell mirror 42 are placed in a cell body 53, and light enters between two of the first cell mirror 41 and second cell mirror 42 through a hole bored in the first cell mirror 41, and the light is multiple-reflected between two of the first cell mirror 41 and second cell mirror 42, and the multiple-reflected light is extracted from the hole bored in the first cell mirror 41. In a gas flow cell 1x illustrated in FIG. 11, in order to smoothly exchange sample-gases, a sample-gas introduction port 18 and a sample-gas exhaust port 19 prepared for sample-gases are arranged in a diagonal direction as recited in JP 2006-58009A. In a configuration of another gas flow cell 1y illustrated in FIG. 12, in which the sample-gas introduction port 18 and the sample-gas exhaust port 19 prepared for sample-gases are arranged on the same side of the cell body 53, the sample-gas introduction port 18 and the sample-gas exhaust port 19 are respectively arranged at portions close to both ends of the cell body 53.
As illustrated in FIGS. 11 and 12, when the sample-gas introduction port 18 and the sample-gas exhaust port 19 prepared for sample-gases are allocated in the diagonal-direction topology or the portions close to both the ends of the cell, and when particles (particulate matters) exist in the sample-gas, as in a semiconductor manufacturing process, a branched tube for the sample-gas introduction port 18 or a branched tube for the sample-gas exhaust port 19 and the first cell mirror 41 and the second cell mirror 42 are closely located. Thus, the particles are easily deposited on surfaces of the first cell mirror 41 and the second cell mirror 42. When the particles are deposited on the surfaces of the first cell mirror 41 and the second cell mirror 42, ascribable to the effect of the multiple-reflection of light, the effective reflection-capabilities of the first cell mirror 41 and the second cell mirror 42 are reduced, and the sensibilities are dropped.
Although the Herriot multiple-reflection cell is represented in FIGS. 11 and 12, another gas-analysis system of absorption-spectrophotometry, such as a gas-analysis system of White multiple-reflection absorption-spectrophotometry and the like, have also similar problems. Furthermore, in optical gas-analysis systems of emission-spectrometry, fluorescent-photometry and the like, other than absorption-spectrophotometry, in general, as in the case of gas analysis of semiconductor manufacturing process, when particles (particulate matters) exist in sample-gas, there is a problem that the particles are apt to be deposited on the surface of a mirror, an optical window or the like, which is disposed at a position close to the branched tube of an inlet or the branched tube of an outlet.
In particular, in the multiple-reflection gas-analysis system, such as the gas-analysis system of the multiple-reflection absorption-spectrophotometry and the like, the effective reflection-capability of the mirror is decreased, as represented by the power of the number of the reflections of light. Thus, because decrease of the effective reflection-capability of the mirror results in a great drop in the sensibility of the gas-analysis system, even a slight particle deposition on the mirror causes the output light quantity from the cell to be decreased to approximately zero.
In view of the above-mentioned problems, an object of the present invention is to provide an optical gas-analysis system and a gas flow cell to be used in the optical gas-analysis system, in which surfaces of mirrors located at both ends of the gas flow cell, an optical window of the gas flow cell, or the like, are prohibited from being contaminated by particles generated in the inside of a process chamber to be examined, from which sample-gas is introduced, so that the sensibility of the optical gas-analysis system is not dropped, and as a result, an accurate gas analysis with high sensibility of the sample-gas in the inside of the process chamber can be achieved and continued, by establishing an accurate in-line monitoring of the sample-gas.